*{
    margin:0;
    padding:0;
}
a{
    text-decoration: none;
    color:black;
}
li{
    list-style:none;
}
body{
    font-family: arial, "Hiragino Sans GB", "Microsoft Yahei", "微软雅黑", "宋体", Tahoma, Arial, Helvetica, STHeiti;
}
header{
    width:100%;
    height:50px;
    background:black;
    color:#fff;
    display: flex;
    justify-content: space-around;
    align-items:center;
}